The invention relates to an automatic testing apparatus for testing the circumferential spacing of gear teeth on the circumference of gear wheels, in which for the testing operation the gear wheel is made to rotate uninterruptedly in one rotational direction at low speed by means of a power source, and in which for the individual testing operations a slide is displaceable on the apparatus frame between stops, which are adjustable if needed, substantially radially toward and away from the gear wheel, the displacement being effected by a drive mechanism. Pivotably supported on the slide are two measuring feelers, the movement of which can be coupled counter to a pre-stressed spring force with the rotational movement of the gear wheel and which cooperate with travel transducers. The measuring feelers are arranged for contact with the same (right to left) flanks of adjacent teeth in the vicinity of the pitch circle of the gear wheel, and indexing means are connected with one of the measuring feelers, which is embodied as the reference feeler, so that at a predetermined measuring position of this feeler, the pickup or output of the measured value by the other measuring feeler is brought about on the one hand, while on the other hand the retraction of the measuring feeler out of the teeth of the gear and its variably retarded reinsertion into the teeth is controllable by indexing the drive mechanism of the slide accordingly.
U.S. patent application Ser. No. 477,785, filed Mar. 22, 1983, now U.S. Pat. No. 4,519,241, which is incorporated herewith by reference addresses the disadvantage in known measuring devices that two complete revolutions of the gear are required to detect errors in circumferential spacing at the right and left tooth flanks in succession and that between the two revolutions the measuring feeler must furthermore be moved over from one tooth flank to the other. This is very expensive in terms of time and money, a cost which moreover, in the case of testing on the gear-cutting machine itself, is considerably increased by the fact that the gear-cutting machine, which has a high hourly output, is not productive during the testing period.